export function createCanvas() {
    var canvas = document.getElementById("canvas");
    var ctx = canvas.getContext("2d");


    var w = canvas.width = window.innerWidth,
    h = canvas.height = window.innerHeight,
    density = 1;
  
    function setup() {
      window.addEventListener('resize', resize);
  
      density = window.devicePixelRatio != undefined ? window.devicePixelRatio : 1.0;
  
      canvas.width = w * density;
      canvas.height = h * density;
  
      canvas.width = w;
      canvas.height = h;
      canvas.scale = density;
  
      ctx.scale(density, density);
  
  
      draw();
    }
  
    function draw() {
      window.requestAnimationFrame(draw);
    }
  
    function resize() {
      w = canvas.width = window.innerWidth;
      h = canvas.height = window.innerHeight;
  
      canvas.width = w * density;
      canvas.height = h * density;
  
      canvas.width = w;
      canvas.height = h;
  
      ctx.scale(density, density);
    }
  
    setup();



    //创建小球的构造函数
    function Ball() {
        this.x = randomNum(3, canvas.width - 3);
        this.y = randomNum(3, canvas.height - 3);
        this.r = randomNum(1, 3);
        this.color = randomColor();
        this.speedX = randomNum(-3, 3) * 0.2;
        this.speedY = randomNum(-3, 3) * 0.2;
    }
    Ball.prototype = {
            //绘制小球
            draw: function () {
                    ctx.beginPath();
                    ctx.globalAlpha = 1;
                    ctx.fillStyle = this.color;
                    ctx.arc(this.x, this.y, this.r, 0, Math.PI * 2);
                    ctx.fill();
                },
                //小球移动
                move: function () {
                    this.x += this.speedX;
                    this.y += this.speedY;
                    //为了合理性,设置极限值
                    if (this.x <= 3 || this.x > canvas.width - 3) {
                        this.speedX *= -1;
                    }
                    if (this.y <= 3 || this.y >= canvas.height - 3) {
                        this.speedY *= -1;
                    }
                }
        }
        //存储所有的小球
    var balls = [];
    //创建200个小球
    for (var i = 0; i < 150; i++) {
        var ball = new Ball();
        balls.push(ball);
    }
    main();
 
    function main() {
            ctx.clearRect(0, 0, canvas.width, canvas.height);
            //鼠标移动绘制线				
            mouseLine();
            //小球与小球之间自动画线
            drawLine();
            //使用关键帧动画，不断的绘制和清除
            window.requestAnimationFrame(main);
        }
        //添加鼠标移动事件
        //记录鼠标移动时的mouseX坐标
    var mouseX;
    var mouseY;
    canvas.onmousemove = function (e) {
        console.log(e)
        var ev = event || e;
        mouseX = ev.offsetX;
        mouseY = ev.offsetY;
    }
        //判断是否划线
 
    function drawLine() {
            for (var i = 0; i < balls.length; i++) {
                balls[i].draw();
                balls[i].move();
                for (var j = 0; j < balls.length; j++) {
                    if (i != j) {
                        if (Math.sqrt(Math.pow((balls[i].x - balls[j].x), 2) + Math.pow((balls[i].y - balls[j].y), 2)) < 80) {
                            ctx.beginPath();
                            ctx.moveTo(balls[i].x, balls[i].y);
                            ctx.lineTo(balls[j].x, balls[j].y);
                            ctx.strokeStyle = "#bbbbbb";
                            ctx.globalAlpha = 0.2;
                            ctx.stroke();
                        }
                    }
                }
            }
        }
        //使用鼠标移动划线
 
    function mouseLine() {
            for (var i = 0; i < balls.length; i++) {
                if (Math.sqrt(Math.pow((balls[i].x - mouseX), 2) + Math.pow((balls[i].y - mouseY), 2)) < 80) {
                    ctx.beginPath();
                    ctx.moveTo(balls[i].x, balls[i].y);
                    ctx.lineTo(mouseX, mouseY);
                    ctx.strokeStyle = "#bbbbbb";
                    ctx.globalAlpha = 0.8;
                    ctx.stroke();
                }
            }
        }
        //随机函数
 
    function randomNum(m, n) {
            return Math.floor(Math.random() * (n - m + 1) + m);
        }
        //随机颜色
 
    function randomColor() {
        return "rgb(" + randomNum(0, 255) + "," + randomNum(0, 255) + "," + randomNum(0, 255) + ")";
    }
}